Usually a .NETconnection string looks like this, you will have your own server, databse names ofcourse.
"Data Source=localhost\sql2012;Initial Catalog=AdventureWorks;
Integrated Security=SSPI"
SSPI stands for Security Support Provider Interface. The SSPI allows an application to use any of the available security packages on a system without changing the interface to use security services. The SSPI does not establish logon credentials because that is generally a privileged operation handled by the operating system.SSPI stands for Security Support Provider Interface. The SSPI allows an application to use any of the available security packages on a system without changing the interface to use security services. The SSPI does not establish logon credentials because that is generally a privileged operation handled by the operating system.
Other than SSPI you can also use "true". Integrated Security actually ensures that you are connecting with SQL Server using Windows Authentication, not SQL Authentication; which requires username and password to be provided with the connecting string.